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Sunday, 1 December 2013

RAS Ringing at Manor Farm Museum, Botley

In the year 2000 I began ringing House Sparrows at Manor Farm Country Park near Botley, Hampshire. Initially the numbers of birds ringed was fairly modest but as more birds were ringed I decided to set up a BTO RAS project. I have previously written about the project on this blog, and it is one of the driving factors why I continue to ring birds at the site. Over the years, the numbers of birds I have ringed has fluctuated quite significantly, this has been due to a number of reasons. The main issue has been work commitments, which has limited the amount of time I could put into the project. But management practices at the site, and accessibility (the site is open to the public) have also played their part.

House Sparrow with Inscribed Darvic Ring

Many years ago I began colour ringing sparrows as I thought that this would increase the recapture rate of the project. Sparrows are very clever and will remember a net site thereby making them difficult to recapture. I began using small plastic colour rings, but it soon became evident that the sparrows were removing them. I then started using overlapped rings, before ultimately settling on overlapped darvic rings with a letter and two numbers inscribed on them.

Graph Illustrating Total Numbers of House Sparrows Ringed per Year (blue) and Retrapped per Year (Red)

Since the year 2000 I have ringed 656 new birds and have retrapped 453. The longest lived individual recorded to date is 4 years 276 days, and the second longest is 4 years 267 days; there have only been three retraps of birds over 4 years during my study. According to BTO data the maximum recorded age is 12 years and 12 days, which was set in 1978, so an individual from this population has someway to go to get to that ripe old age. There have been several theory's about the decline of the House Sparrow including changes in farming practices (increased use of pesticides, cleaner farming, and changes in cropping regimes), loss of nesting sites and increases in predator species such as sparrowhawk. At Manor Farm these changes have not really occurred but nonetheless the population seems to be declining. I have witnessed sparrowhawks taking birds from a recently flailed hedge, so maybe that is the cause here.

Ageing House Sparrows after their post juvenile/post breeding moult is not possible since the extent of the moult is complete for both adults and juveniles. I have not previously looked in detail at ageing birds, but there have been several suggestions by various authors in the past describing how to separate first year from second year birds. These include a less pure grey crown and broader chestnut edges in first year birds, a difference in the pattern on the upper middle secondary covert, and the colouration of the bill, specifically the yellow bill colour and fleshy lateral lobes at the base of the bill.

Two male house sparrows, note the all dark bill and paler check of the left hand bird, but the yellow base and grey check to the right hand bird

Over the last few weeks have started looking at the bill on some of the birds I have captured, although at this stage I cannot make any assessments as I am catching mainly new birds. However, in male birds I have noticed considerable variation in the colouration of the bill. This is illustrated above where the bird on he left has an all dark bill, and also a more defined head pattern and a whiter cheek. However the bird on the right has a paler bill with yellow at the base, a less well defined head pattern and greyer cheek. Unfortunately both birds were new birds so I could not confirm my suspicions that the bird on the left is an adult.

Adult male House Sparrow which was originally ringed on 2nd January 2010 and retrapped on 30th November 2013 (3 years 332 days later)

One male bird that I retrapped this weekend was originally ringed on 2nd January 2010 (image above). Like the left hand bird in the previous image this bird had a mainly black bill, although not as dark as that bird, and a clearly defined head pattern. Interestingly this bird also exhibited a very well marked black face mask and dark lores. The cheeks are pale grey in colouration.

This male again had an ill-defined head pattern, pale horn coloured bill with a yellow base

The image above illustrates another male bird, this time with an ill-defined head pattern and black mask, paler horn coloured bill with a yellow base. The cheeks on this individual are quite pale, but appeared slightly buff coloured as opposed to the dark billed birds which were greyer. I have yet to look in detail at female birds, but of the ones that I did the bill colour seemed to be fairly consistent, being dull pink in colouration with a yellow base. Over the next couple of years I will look more closely at this and maybe by the end I will be able to confidently separate adult and juvenile birds.

Female House Sparrow with dull pink bill and a yellow base.

In two sessions this weekend I caught 50 new birds and retrapped 12, of 10 species. The new species included 28 house sparrows, eight goldfinches, five blackbirds, three robins, two blue tits and single wren, great tit, nuthatch and carrion crow. Of the retraps the most notable were a long-tailed tit, that was originally trapped 2 years and 270 days previously, a blue tit that was originally ringed 2 years 269 days previously and three House Sparrows that were ringed 4 years 276 days, 3 years 332 days and 3 years 156 days previously.